var left="牛奶"
var right="奶茶"
var temp;
//let定义块级变量
{
    let a=100
    console.log(a)
    // let username='admin'
}
let username='admin'
//const定义常量
const PI=3.14
const user={}
left=right
temp=left
right=temp
console.log(left,right);
console.log(username)
// console.log(a)